Monolithic vacuum manometer utilizing electrostatic interference as a means of detection

ABSTRACT

A monolithic manometer and method of sensing pressure changes may include sensing a change in parasitic capacitive coupling between multiple parasitic capacitive coupled conductive elements in response to a diaphragm disturbing the parasitic capacitive coupling between the conductive elements. A signal representative of the sensed change in parasitic capacitive coupling may be output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application for patent claims priority from U.S. ProvisionalApplication Ser. No. 61/222,184, filed Jul. 1, 2009; the entireteachings of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Many industrial processes may only be performed at low pressures. Suchprocesses include, but are not limited to, semiconductor manufacturing,micro machining, vacuum deposition, and specialized coatings. In manysuch processes, pressure regulation is critical in order to maintainenvironmental conditions (e.g., temperature and pressure), a manometer,which is a type of pressure sensor, may be utilized. The manometer isconfigured to sense pressure changes in a process chamber that hasreduced pressure.

One type of manometer that is sensitive enough to measure pressures assuch low pressures is a diaphragm-based manometer. Diaphragm-basedmanometers are widely used in the semiconductor industry. In part, thisis because diaphragm-based manometers are typically well suited to thecorrosive services of this industry due to having high accuracy andbeing resistant to contamination. In particular, diaphragm-basedmanometers exhibit enhanced resistance to contamination and operatelonger without maintenance.

A manometer serves as the vacuum/pressure sensing element and may beused to measure and/or control the pressure within a process chamber. Adiaphragm-based manometer typically has a housing containing twochambers separated by a circular tensioned diaphragm. The first chamberis in fluid communication with the process chamber or other assembly inwhich the pressure is to be measured. The second chamber of thediaphragm-based manometer is commonly referred to as the referencechamber and is typically (although not necessarily) evacuated and sealedat a pressure that is substantially less than the minimum pressure thesensor senses.

A diaphragm, which is generally circular, is tensioned and separates thetwo chambers within a housing of the diaphragm-based manometer. Thediaphragm is essentially formed of a thin metal that is mechanicallyconstrained about its periphery. The diaphragm reacts to differentialpressures by deforming into a bowed shape with the periphery remainingstationary. The diaphragm, thereby, serves as a flexing, groundedelectrode. The diaphragm deforms as a reaction to the pressuredifference across it and also interacts with electrostatic fields suchthat the deformation of the diaphragm may be resolved through theseelectrostatic interactions.

In close proximity to the diaphragm lies an electrode assembly. Thisassembly generally includes a stiff platform with a polished,electrically insulating surface that bears two conductive electrodes.The conductive electrodes are typically silk screen painted onto thesurface, which is often a ceramic base. The configuration of theconductive electrodes of conventional diaphragm-based manometersgenerally includes an inner, solid circle and a ring that encircles theinner circle. The electrode assembly is mechanically constrained a fixeddistance from the plane containing the periphery of the diaphragm sothat the electrodes are very close to the diaphragm (<0.005 in) and runparallel to the surface of the diaphragm. Flexure of the diaphragm, dueto applied pressure, can easily be computed by measuring the capacitanceto ground at each electrode and subtracting one measurement fromanother.

Modern diaphragm-based manometers utilize two electrodes to monitor theflexure of the diaphragm. The capacitance to ground of the twoelectrodes (“common-mode capacitance”) varies with flexure of thediaphragm, but also changes with movement of the electrode assembly.Such movement occurs with temperature changes, temperature transients,and mechanical loading. Measurements using the difference in capacitanceof the two plates (“difference capacitance”) are more stable since theyreject motions between the diaphragm and electrodes and instead reflectthe deflection of the diaphragm.

As the diaphragm is displaced, capacitance between the diaphragm and theconductive elements changes. The changing capacitance causes a change incharge being sensed from the two conductive elements, thereby providinga measurement to determine a change in pressure in the process chamber.The measured pressure change may be used for altering the environmentalconditions by a controller of the vacuum chamber.

Diaphragm-based manometers are very precise. However, as a result, themanometers have components and tolerances that, too, are very precise.Generally speaking, there are a fair number of components inconventional diaphragm-based manometers that are used to (i) reducetemperature variation effects (e.g., thermal expansion and contraction)that impact repeatability of the manometer, (ii) reduce straycapacitance effects on measurement, (iii) reduce alignment variations ofthe components in the manometer, and so forth. As a result, the cost andproduction of the manometers are challenges that have plaguedmanufacturers for years. As an example, as thermal effects causeexpansion and contraction of materials of the manometer, such as a metalhousing and support hardware for the ceramic base, thermal cycles causedifferent readings at the same temperature on different sides of thethermal cycles as the materials themselves are slightly repositionedwith respect to one another, even if formed of the same material, due tothermal conductivity rates not being identical. As understood, as aresult of the production and repeatability issues, manufacturingdiaphragm-based manometers is labor intensive and costly.

SUMMARY OF THE INVENTION

The principles of the present invention overcome many of the problems ofconventional manometers by (i) using a monolithic design in which thebase serves as the housing, thereby reducing thermal effects, (ii) usinga glass coating on which conductive elements are formed usingphotolithographic processes, thereby improving sensitivity, (iii)electrostatically interfering with parasitic capacitance between theconductive elements by the diaphragm (as opposed to measuring changes incapacitance between the conductive elements and the conductive elementsas performed by conventional manometers), thereby increasing sensitivityto pressure changes, and (iv) grounding a sensor circuit to the housing,thereby reducing stray capacitance effects and reducing complexity ofthe manometer. By using these structural and electrical configurations,and other manufacturing processes to manufacture the manometer, themanometer may be significantly less complex and less costly to produce,be capable of being produced in a large scale manufacturing process, andbe less sensitive to environmental changes, thereby being morerepeatable over time and being less expensive to manufacture.

One embodiment of a vacuum manometer may include a base including a sidewall extending higher than a center portion including a top surface anda bottom surface. Multiple conductors may extend through openingsdefined by the center portion of the base. A glass coating may beattached to at least a portion of the top surface of the base.Conductive elements may be disposed on the glass coating and inelectrical communication with said electrical conductors. A diaphragmmay be connected to the side wall and extend over the conductiveelements.

One embodiment of a method of sensing pressure changes may includesensing a change in parasitic capacitive coupling between multipleparasitic capacitively coupled conductive elements in response to adiaphragm disturbing an electrostatic field between the parasiticcapacitively coupled conductive elements. A signal representative of thesensed change in parasitic capacitive coupling may be output.

Another embodiment of a vacuum manometer may include a monolithic baseincluding a top surface and side wall extending higher than the topsurface. Multiple conductive elements may be supported by the topsurface of the base. A diaphragm may be connected to the side wall ofthe monolithic base and positioned above the conductive elements withrespect to the top surface of the monolithic base. A cover may beconfigured to cover the base above the diaphragm.

One embodiment of an electrical circuit for measuring pressure changeson a vacuum manometer may include an oscillator generating anoscillating signal. An inverter may be electrically connected to theoscillator, and configured to invert the oscillating signal beinggenerated by the oscillator. A first conductive element in electricalcommunication with the oscillator, the oscillating signal being appliedto the first conductive element. A second conductive element may be inelectrical communication with the inverter, where the invertedoscillating signal may be applied to the second conductive element. Athird conductive element may be in parasitic capacitive coupling withthe first and second conductive elements. Sensor circuitry may be inelectrical communication with the third conductive element, and beconfigured to measure charge on the third conductive element.

One embodiment of a method of manufacturing a vacuum manometer mayinclude receiving a base having a top surface including multipleconductors extending through the base and above the top surface of thebase. A glass coating may be applied onto the top surface of the base.The glass coating may be flattened to form a flat glass surface. Theflattening may cause the conductors to be altered such that respectiveexposed portions of the conductors are substantially co-planar with theflat glass surface. Multiple conductive elements may be applied onto theflat glass surface, the conductors being connected to respectiveconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the system and methods of theprinciples of the present invention may be obtained by reference to thefollowing Detailed Description when taken in conjunction with theaccompanying Drawings wherein:

FIG. 1 is an illustration of an illustrative vacuum manometer configuredto sense pressure changes in a vacuum chamber utilizing parasiticcapacitive coupling;

FIG. 2 is an illustration of an illustrative base having conductiveelements disposed thereon, and having parasitic capacitive couplingbetween the conductive elements;

FIG. 3 is a block diagram of illustrative circuitry in communicationwith conductors having parasitic capacitance coupling therebetween;

FIG. 4 is an illustration of illustrative conductor elements for use insensing changes in pressure in a vacuum chamber;

FIG. 5 is an electrical schematic of an illustrative circuit used indriving and sensing conductor elements, such as those shown in FIG. 4,for sensing pressure changes by a diaphragm-based manometer;

FIG. 6 is an illustration of an illustrative manometer showing portionsof sensor circuitry, base, and conductive elements for use in sensingchanges in pressure by the manometer;

FIG. 7 is a signal diagram showing illustrative dryer signals andmeasured signal based on diaphragm position of a diaphragm-basedmanometer in accordance with the principles of the present invention;

FIGS. 8A-8E (collectively FIG. 8) are illustrations of different stagesof manufacturing a diaphragm-based manometer in accordance with theprinciples of the present invention; and

FIG. 9 is a flow diagram of an illustrative process for operation of adiaphragm-based manometer for sensing pressure changes in accordancewith the principles of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With regard to FIG. 1, an illustration of an illustrative manometer 100is shown to include a machined base 102 and cover 104. The machined base102 may be a metallic base that is formed of a pure metal or compositealloy. In one embodiment, the machined base 102 has a low thermalcoefficient of expansion. The machined base 102 may use a metal alloy,such as Inconel® alloy produced by Special Metals Corporation of NewHartford, N.Y. The cover may be metallic and, also, may be Inconel®alloy material. The cover 104 is shown to include a tube 105 to whichanother tube or other element may be connected to a vacuum chamber sothat the manometer 100 may sense pressure changes in the vacuum chamber.By having each of the components of the manometer, including the base102 and cover 104, be the same material, the manometer 100 is consideredto be monolithic. Because the manometer 100 is monolithic, the manometer100 has significantly fewer repeatability and operational problems asconventional non-monolithic manometers.

The machined base 102 may include a mesa section 106 that has a topsurface 107. A diaphragm 108 may also be formed of a metal or metalalloy, such as Inconel® alloy, as previously described herein above. Aglass-coated, insulating layer 110 may be disposed on the top surface107 of the mesa 106 of the base 102. The glass coating 110 may beconnected to the top surface 107 and may have conductive elements orconductors 112 a-112 c (collectively 112) to deposited thereon usingvapor deposition and photolithography processes, as understood in theart.

Glass feed-throughs 114 a-114 c (collectively 114) may be extendedthrough openings defined by the mesa 106 of the base 102. The glassfeed-throughs 114 include glass elements 116 a-116 c (collectively 116)and conductors 118 a-118 c (collectively 118) that extend through themesa section 106 of the base 102. In one embodiment, the glassfeed-throughs are created using a powdered form of glass and processedby heating or otherwise to form glass frits in the openings. Theconductors 118 may be used to connect conductive elements 112 to sensorcircuitry (see, FIG. 5).

The base 102 also includes sidewall 119 that extends higher than themesa section 106 to enable the diaphragm 108 to be connected thereto andpass over the conductors 112 supported by the mesa section 106. A cantedring 120 may be disposed above the sidewall 119 and enable the diaphragm108 to be connected and sandwiched between the canted ring 120 andsidewall 119 at connection point 122. In one embodiment, the manometer100 has a circular base 102 that uses a circular diaphragm. A seal 124may be a welding directly connecting the base 102 and cover 104.

With regard to FIG. 2, an illustration of an illustrative portion 200 ofa manometer is shown to describe operation of the manometer. A topsurface 202 of a base is shown to include a glass coating 203 that isconnected to the top surface 202. It should be understood that a coatingother than a glass coating that is capable of being smoothed to aflatness that meet specifications for a diaphragm-based manometer may beutilized to provide for the principles of the present invention.Conductive elements 204 may be utilized to provide pressure sensingcapabilities by having parasitic capacitive couplings 206 a-206 n(collectively 206) between the conductive elements 204, as furtherdescribe herein. The parasitic capacitive couplings 206 provide forelectrostatic interference between the conductive elements 204. As airmolecules hit the diaphragm 208, which causes pressure 210 on thediaphragm 208, the diaphragm 208, which has its weakest point in thecenter of the diaphragm 208, is deflected in the center in a parabolicmanner, thereby causing the parasitic capacitive couplings 206 to beinterfered with in the center of the conductive elements 204.

Conductors lines 212 a and 212 b may have + phase and − phase signalsapplied to the conductor lines 212 a and 212 b, respectively. The +phase signal is shown to be on conductor line 212 a, which may beconnected to conductor elements 204 in the center of the phase lines204. When the pressure 210 deflects or displaces the diaphragm 208 inthe center of the conductive elements 204 to cause center parasiticcapacitive couplings to be electrostatically interfered with, a senseline 214 that is connected to one of the conductive elements 204 that isparasitically capacitively coupled with both the conductive element thathas the + phase signal applied thereto in the center of the conductorelements 204 and − phase signal in the outer region of the conductorelements 204 collects a higher number of charges from the − phase signalwhen the pressure 210 increases on the diaphragm 208.

With regard to FIG. 3, a schematic block diagram of illustrative sensorcircuitry that includes both drive circuitry and sense circuitry isshown. In addition, a first conductive element 302 a, second conductiveelement 302 b, and third conductive element 302 c are shown. Each ofconductive elements 302 a are different parts of a single conductiveelement. The same holds true for conductive elements 302 b and 302 c.Parasitic capacitive coupling 304 a and 304 b are shown between thefirst conductive element 302 a and conductive element 302 c and thesecond conductive element 302 b and conductive element 302 c. The thirdconductive element 302 c is interdigitated with conductive elements 302a and 302 b (See, FIG. 4).

An oscillator 306 is configured to generate an oscillatory signal, suchas a square wave. An oscillator signal 310, which is a + phase signal,is communicated onto conductor line 312. The oscillator signal 310 isalso communicated to inverter 308, which applies an inverted oscillatorsignal or − phase signal 314 onto conductor line 316. Conductor line 312is in electrical communication with conductive element 302 a andconductor line 316 is in electrical communication with conductiveelement 302 b. A conductor line 318 is in electrical communication withconductive element 302 c, and configured to receive charges 320 that arecollected by the conductive element 302 c from the parasitic capacitivecoupling 304 b with conductive element 302 b. A differential signal 322,which is generated by the charges 320, is a lower amplitude signal thanthe inverted oscillator signal 314 and matches phase and frequency ofthe inverted oscillation signal 314 as a result of the parasiticcapacitive coupling 304 b.

A sensor circuit 324 may be configured to receive the differentialsignal 322 for processing and outputting an output signal 326 onto anoutput line 328. In one embodiment, the sensor circuit 324 is configuredto generate the output signal at a full scale pressure (FSP) amplitudein response to maximum pressure being applied to the diaphragm and nosignal in response to the diaphragm being at a null position whenpressure in the vacuum is at a steady state pressure. The output signal326 may be communicated and used by a controller (not shown) of a vacuumchamber, such as a mass flow controller, for use in maintaining oradjusting environmental parameters (e.g., temperature and pressure) inthe vacuum chamber being sensed by the manometer.

With regard to FIG. 4, an illustrative set of conductive elements 400 isshown. In this embodiment, three conductive elements are used. A − phasefeed-through conductor 402, + phase feed-through conductor 404, andsense line feed-through conductor 406 are shown to be connected to threedifferent conductive elements or trace lines. The traces lines include −phase conductive element 408 that includes a linear portion extendingradially inward from the − phase feed-through conductor 402 and curvedportions 408 a-408 n that extend from the linear portion of the − phaseconductive element 408. A + phase conductive element 410 has a linearportion that extends radially outward from the + phase feed-throughconductor 404 in the center of the conductive elements 400 and hascurved portions 410 a-410 n that extend from the linear portion of the +phase conductive element 410. A sense line conductive element 412 has alinear portion that extends radially inward from the sense linefeed-through conductor 406 and has curved portions 412 a-412 n thatextend from the linear portion of the sense line conductive element 412.

The curved portions 412 a-412 n may be interdigitated with the curvedportions 408 a-408 n of the − phase conductive element 408 and curvedportions 410 a-410 n of the + phase conductive element 410. Thisinterdigitization of the curved portions of the conductive elements 408,410, and 412 provides for the parasitic capacitive coupling between (i)the − phase conductive element 408 and sense line conductive element412, and (ii) the + phase conductive element 410 and sense lineconductive element 412. As the + phase conductive element 410 ispositioned toward the center of the conductive elements 400 with respectto the − phase conductive element 408, when a diaphragm (not shown) isdisplaced toward the conductive elements 400 in the center region abovethe conductive elements 400, the parasitic capacitive coupling betweenthe + phase conductive element 410 and sense line conductive element 412is disturbed, thereby causing the parasitic capacitive coupling betweenthe + phase conductive element 410 and sense line conductive element 412to be reduced. When the parasitic capacitive coupling of the + phaseconductive element 410 and sense line conductive element 412 is reduced,the sense line conductive element 412 receives more charges from the −phase conductive element 408 than from the + phase conductive element410.

With regard to FIG. 5, a schematic of illustrative sense circuitry 500is shown to include excitation circuitry 502, a charge collector 504, asynchronous detector 506, and sensor offset circuitry 508. Theexcitation circuitry 502 may include an oscillator (not shown) that isconfigured to generate an oscillatory signal, such as a square wave, anda buffer 510 and inverter 512 to generate a + phase signal 514 and −phase signal 516, respectively.

The charge amplifier 504 may include an op amp 518 and capacitor 520,which combine to operate as an integrator to integrate or sum current orcharges being applied to the op amp 518. A DC feedback path 522 may beconfigured to maintain a DC portion of the feedback stable to preventthe op amp 518 from becoming saturated in either a positive or negativeside. A ground line 524 connected to the positive input terminal of theop amp 518 may be used to eliminate or reduce shielding from a substrateof the sensor from stray capacitance. In one embodiment, the ground line524 is connected to the base of the manometer, as shown in FIG. 6.

The synchronous detector 504 may include a multiplier 526 and sample andhold component 528 to synchronize the excitation (+ phase signal 514)and output signal 530 from the charge amp 504, which, as a result of theinverted op amp 518 being used, is positively phased. The sample andhold component 528 may measure a value of the sense line 532 to generatea pressure signal or output signal 534 that may be filtered usingcapacitor 536.

The sensor offset circuitry 508 may include a potentiometer 538 that isconfigured to be adjusted to balance the + phase signal 514 and − phasesignal 516. A voltage divider 540 may be utilized to substantiallyreduce amplitude of a first stage offset signal 542 from thepotentiometer 538 by a couple of orders of magnitude to generate asecond stage offset signal 544. By reducing the magnitude of the firststage offset signal 542, a capacitor 546 may be chosen to besignificantly large enough (e.g., between approximately 5 andapproximately 10 pico Farads) to remove leakage capacitance and leakagecurrents that would otherwise be passed into the sense line 532. Asecond stage offset signal 544 is output from the voltage divider 540and results in a third stage offset signal 548 after passed across thecapacitor 546.

With regard to FIG. 6, an illustration of a portion 600 of a manometeris shown. The portion 600 of the manometer is shown to combine multipleaspects of the portions from previous figures to summarize functionalityof the manometer in accordance with the principles of the presentinvention. A base 602 is shown to have a top surface 603 above which adiaphragm 604 is shown to be connected to a sidewall 605 of the base602. Circuitry 606 is also provided and is shown to be in communicationwith conductive elements 608 a-608 n, 610 a-610 n, and 612 a-612 n,where each of the conductive elements 608 a-608 n, 610 a-610 n, and 612a-612 n are interdigitated “fingers” of respective conductive elements.The conductive elements 608 a-608 n, 610 a-610 n, and 612 a-612 n areillustrative in that the actual conductive elements would be disposed onthe top surface 603 of the base 602 in a format as illustrated in FIG.4, for example. Between the conductive elements 608 a-608 n and 612 aare parasitic capacitive couplings 614 a-614 n that allow charges fromthe conductive elements 608 a-608 n to be collected by the conductiveelement 612 a. Similarly, conductive elements 610 a-610 n and 612 n haveparasitic capacitive couplings 616 a-616 n therebetween to enable theconductive element 612 n to receive charges from the conductive elements610 a-610 n when a signal is applied thereto (e.g., oscillating signal).

In operation, oscillator 618 generates an oscillating signal 620 andinverter 622, which is connected to the oscillator 618, causes theoscillating signal 620 to be inverted to become an inverted oscillatingsignal 624. Conductor line 626 is connected to conductive elements 610a-610 n to apply the oscillating signal 620 thereto, and conductor line628 is in electrical communication with conductive elements 608 a-608 nto allow the inverted oscillating signal 624 to be applied to theconductive element 608 a-608 n. Glass feed-throughs 630 a-630 c areextended through the base 602 to enable the conductor lines 626 and 628to be in electrical communication with conductive elements 610 a-610 nand 608 a-608 n, respectively. In addition, a conductor line 632, whichis in electrical communication with conductive elements 612 a-612 n viaglass feed-through 630 b, receives charges 634 for input into sensorcircuitry 636. Ground line 638 may also be connected to the sensorcircuitry 636 and to base 602. As such, stray capacitance 640, which isinherent in any system, but particularly relevant with manometers, ismitigated in its effect. By using the ground line 638, coaxial cablesthat are generally used in conventional manometers to prevent straycapacitance from affecting measurements by the manometer may beeliminated. The sensor circuitry 636 may output a sensor signal 642 onoutput line 644.

With regard to FIG. 7, a + phase signal 702 and − phase signal 704 areshown to be synchronized with one another. A diaphragm position curve706 is also shown. At time T0, the diaphragm position curve 706 is shownto move from a null position as pressure is applied to the diaphragm. Asthe diaphragm is increased in position from a null position by pressurebeing applied to the diaphragm, the diaphragm eventually reaches afull-scale pressure position, which causes a measured signal 708 toreach a maximum amplitude that corresponds with the − phase signal attime T1. As the pressure reduces on the diaphragm, the diaphragmposition curve 706 is shown to return to a null pressure at time T2,which causes the measured signal 708 to be to zero at time T3.

With regard to FIGS. 8A-8E, a flow chart of an illustrativemanufacturing process and manometer configuration at the manufacturingprocess stage are shown. With regard to FIG. 8A, the process starts atstep A, where a machined base 800 a is received. The machined base 800 amay be the base itself or be a base that has some amount of processingalready performed. The machined base 800 a may be metallic or metalalloy. By being machined, cost may be reduced as compared to alternativebase materials, such as ceramic. The machined base 800 a is shown tohave glass feed-throughs 802 a-802 c installed at step B. The glassfeed-throughs 802 a-802 c may include conductors 804 a-804 c,respectively. The glass feed-throughs 802 a-802 c extend throughopenings defined by a mesa 806 of the machined base 800 a. In oneembodiment, the glass feed-throughs are applied to the base 800 a afterreceiving. At step C, the machined base 800 a may be fired or heatedsuch that microscopic crystals in the machined base 800 a are released,which reduces deformation due to heating and cooling cycles whenoperating in a manometer.

With regard to FIG. 8B, at step D, a glass coating 808 is applied to atop surface of the mesa 806 of the base 800 b. The glass coating 808 maybe applied as a tape casting, which is a mix of glass in a slurry formwith organic binders that are formed into a sheet. Other forms of glass,including liquid glass or any other glass form, may be applied, as shownin FIG. 8B.

With regard to FIG. 8C, at step E, the applied glass may be ground tobecome flat to produce a flat glass surface 808′ on the base 800 c. Withthe grinding of the glass 808, the glass feed-throughs 802 a-802 c arealso ground. In addition, the conductors 804 a-804 c, too, are groundsuch that the glass coating 808′, glass feed-through or flit 802 a-802c, and conductors 804 a-804 c become coplanar.

With regard to FIG. 8D, at step F, a metal layer 810 may be applied overthe glass layer 808′. The metal layer 810 may be deposited using a vapordeposition process, such as one used in the production of semiconductorchips. At step G, a photolithographic process may be performed toproduce trace lines that are conductive elements, as described herein(see FIG. 4). The photolithographic process may include etching andother processes that are used in the production of semiconductor chips,as understood in the art. The manufacturing process described in FIG. 8allows for mass production of manometers, as each of the bases of themanometers may be placed in a single tray and the manufacturingoperations may be performed on multiple manometers simultaneously.

With regard to FIG. 9, a flow diagram 900 of an illustrative process foroperation of a manometer in accordance with the principles of thepresent invention is shown. At step 902, a change in parasiticcapacitive coupling between parasitic capacitive coupled conductiveelements in response to a diaphragm disturbing the parasitic capacitancecoupling between the conductive elements may be sensed. In disturbingthe parasitic capacitance coupling, an electrostatic field that createsthe parasitic capacitance coupling may be altered by the diaphragmentering the field. The sensing may cause charges to be sensed from asense line by a sense circuit. At step 904, a signal representative inthe change in parasitic capacitive coupling may be output from themanometer.

It should be understood that the description and drawings areillustrative and that alternative structure and processes may beutilized to perform the same or analogous functionality in accordancewith the principles of the present invention. For example, alternativecircuitry may be utilized to change phase or types of signals, butresult in the same output. Still yet, different trace lineconfigurations of the conductive elements may be utilized and,optionally, compensated for by the circuitry. In addition, alternativemanufacturing processes may be utilized to produce a diaphragm-basedmanometer in accordance with the principles of the present invention.

The previous detailed description of a small number of embodiments forimplementing the invention is not intended to be limiting in scope. Oneof skill in this art will immediately envisage the methods andvariations used to implement this invention in other areas than thosedescribed in detail. The following claims set forth a number of theembodiments of the invention disclosed with greater particularity.

1. A vacuum manometer, comprising: a base including a side wall extending higher than a center portion including a top surface and a bottom surface; a plurality of conductors extending through openings defined by the center portion of said base; a glass coating attached to at least a portion of the top surface of said base; a plurality of conductive elements disposed on said glass coating and in electrical communication with said electrical conductors; and a diaphragm connected to the side wall and extending over said conductive elements.
 2. The vacuum manometer according to claim 1, wherein said conductive elements are vapor deposition deposits on said glass coating.
 3. The vacuum manometer according to claim 1, further comprising a plurality of glass feed-throughs connecting to inside surfaces of the openings through which said conductive conductors respectively pass, the glass feed-throughs providing vacuum tight seals.
 4. The vacuum manometer according to claim 1, wherein there are three electrical conductors.
 5. The vacuum manometer according to claim 4, further comprising circuitry in electrical communication with said three conductors, said circuitry configured to (i) drive two of said conductors with respective alternating electrical signals that are opposite in phase and have substantially the same amplitude, and (ii) receive a net charge induction signal in response to said diaphragm moving.
 6. The vacuum manometer according to claim 5, wherein said circuitry is configured to collect charge in response to said diaphragm interfering with parasitic capacitive coupling between two of the conductive elements in electrical communication with the two conductors on which the alternating electrical signals are being driven.
 7. The vacuum manometer according to claim 5, wherein said conductive elements include three interdigitated conductive elements.
 8. The vacuum manometer according to claim 7, wherein: a first interdigitated conductive element extends in substantially circular directions from a first linear conductive strip extending radially inward from a first one of said conductors extending through said base; a second interdigitated conductive element extends in substantially circular directions from a second linear conductive strip extending radially outward from a second one of said conductors extending through said base; and a third interdigitated conductive element extends in substantially circular directions from a third linear conductive strip extending radially inward from a third one of said conductors extending through said base.
 9. The vacuum manometer according to claim 8, wherein one of the two conductors with alternate electrical signals is connected to the first interdigitated conductive element, the other of the two conductors with alternate electrical signals is connected to the second interdigitated conductive element, and the third conductor is connected to the third interdigitated conductive element.
 10. The vacuum manometer according to claim 1, wherein said base is metallic.
 11. A method of sensing pressure changes, said method comprising: sensing a change in parasitic capacitive coupling between a plurality of parasitic capacitive coupled conductive elements in response to a diaphragm disturbing the parasitic capacitive coupling between the conductive elements; and outputting a signal representative of the sensed change in parasitic capacitive coupling.
 12. The method according to claim 11, wherein sensing includes collecting a differential charge in response to the diaphragm crossing an electrostatic field that provides for the parasitic capacitive coupling between the conductive elements.
 13. The method according to claim 11, wherein sensing includes sensing a differential change in the parasitic capacitive coupling between (i) a first signal line and a sense line and (ii) a second signal line and the sense line.
 14. The method according to claim 11, further comprising blocking stray capacitance by using a ground line for circuitry configured to perform said sensing.
 15. The method according to claim 11, further comprising: applying a first oscillating signal onto a first conductive element of the conductive elements; applying a second oscillating signal onto a second conductive element of the conductive elements, the second oscillating signal being 180 degrees out of phase from the first oscillating signal; and wherein sensing includes collecting charge as a result of more positive parasitic capacitive coupling being disturbed than negative parasitic capacitive coupling.
 16. A vacuum manometer, comprising: a monolithic base having a top surface and side wall extending higher than the top surface; a plurality of conductive elements supported by the top surface of said base; a diaphragm connected to the side wall of said monolithic base and positioned above said conductive elements with respect to the top surface of said monolithic base; and an enclosure configured to cover said base above said diaphragm.
 17. The vacuum manometer according to claim 16, further comprising a glass layer connected to said monolithic base, and wherein said conductive elements are connected to said glass layer.
 18. The vacuum manometer according to claim 16, further comprising an electrical circuit connected to said conductive elements and configured to sense a change in parasitic capacitive coupling between conductive elements in response to said diaphragm moving in response to a change in pressure.
 19. The vacuum manometer according to claim 18, where in said monolithic base is configured to enable said electrical circuit to produce the substantially same measurement when said base is a given temperature after one or more thermal cycles.
 20. An electrical circuit for measuring pressure changes on a vacuum manometer, said electrical circuit comprising: an oscillator generating an oscillating signal; an inverter electrically connected to said oscillator, and configured to invert the oscillating signal being generated by said oscillator; a first conductive element in electrical communication with said oscillator, the oscillating signal being applied to said first conductive element; a second conductive element in electrical communication with said inverter, the inverted oscillating signal being applied to said second conductive element; a third conductive element being in parasitic capacitive coupling with said first and second conductive elements; and sensor circuitry in electrical communication with said third conductive element, and configured to measure charge on said third conductive element.
 21. The electrical circuit according to claim 20, wherein said sensor circuitry includes a charge amplifier circuit configured to generate a voltage in response to receiving charges from said third conductive element.
 22. The electrical circuit according to claim 20, wherein said sensor circuitry is grounded to a base of the vacuum manometer, and wherein said sensor circuitry is guarded from stray capacitance by the ground.
 23. The electrical circuit according to claim 20, wherein said sensor circuitry includes sensor offset circuitry in electrical communication with said oscillator and said inverter, and configured to receive the oscillating signal as a first input signal and the inverted oscillating signal as a second input signal, said sensor offset circuitry including: a variable adjustment circuit element configured to enable a user to variably adjust between the first and second input signals to generate a first stage offset signal; a voltage divider configured to reduce signal level of the first stage offset signal to generate a second stage offset signal; and a capacitive element electrically connected to said voltage divider and configured as a differentiating element to ensure that a third stage offset signal is of appropriate phase, the third stage offset signal being applied to an input signal line of said sensor circuitry connected to said third conductive element.
 24. The electrical circuit according to claim 20, wherein said sensor circuitry includes: a synchronous detected circuit including a multiplier having a first input line and a second input line, the first input line receiving a charge voltage signal from a charge collector circuit of said sensor circuitry and the second input line receiving the oscillating signal from said oscillator, the multiplier multiplying the charge voltage signal and oscillating signal to generate a synchronous detected signal; and a sample and hold circuit configured to generate a detected signal representative of a pressure change at the manometer.
 25. A method of manufacturing a vacuum manometer, said method comprising: receiving a base having a top surface and a plurality of conductors extending through the base and above the top surface of the base; applying a glass coating onto the top surface of the base; flattening the glass coating to form a flat glass surface, the flattening causing the conductors to be altered such that respective exposed portions of the conductors are substantially co-planar with the flat glass surface; and applying a plurality of conductive elements onto the flat glass surface, the conductive elements being connected to respective conductors.
 26. The vacuum manometer according to claim 25, further comprising flattening the top surface of the base prior to applying the glass coating.
 27. The vacuum manometer according to claim 25, wherein applying the glass coating includes: placing a glass material onto the top surface of the base; and heating the base and glass material to cause the glass material to flow; and cooling the glass.
 28. The vacuum manometer according to claim 25, wherein applying the conductors onto the flat glass surface includes using a photolithographic process to define trace lines of the conductors.
 29. The vacuum manometer according to claim 25, wherein applying the conductors includes applying three, interdigitated conductors to the flat glass surface.
 30. The vacuum manometer according to claim 25, further comprising assembling glass feed-throughs including the conductors extending, and wherein flattening the glass coating includes flattening at least a portion of the glass feed-throughs to cause top surfaces of the glass feed-throughs to be substantially co-planar with the flat glass surface. 